Synthetic fibrous unit which is three-dimensionally crimped and twisted

ABSTRACT

A three-dimensionally crimped and twisted synthetic fibrous unit formed by a stem having a relatively large width. Branches randomly extend from the stem and have a width less than the stem width, and fine hairs randomly extend from the branches. Numerous peripherally and internally formed crevices are provided in the fibrous unit.

United States Patent [191 Maki [451 Feb. 11, 1975 1 SYNTHETIC FIBROUSUNIT WHICH IS THREE-DIMENSIONALLY CRIMPED AND TWISTED [75] inventor:Isao Maki, Tokyo, Japan [73] Assignee: Soko Co., Ltd., Tokyo. Japan [22]Filed: June 14, 1972 [21] Appl. No.: 262,635

Related U.S. Application Data [63] Continuation in-part of Ser. No.24,658. April 1,

1970, abandoned.

[52] U.S. C1 57/140 ,1, 161/173, 161/177, 161/179, 161/180, 225/93,225/965.

264/Dig. 47, 264/D1G. 147, ZS/Dig. 1 F

[51] Int. Cl 002g 3/00, D02g 3/02 [58] Field of Search 161/172, 173,177, 179, 161/180, 169; 57/140 .1

[561 References Cited UNITED STATES PATENTS 3,423,284 1/1969 Marek eta1. 162/157 3,506,535 4/1970 Prevorsek et a1. 161/177 3,551,275 12/1970Teng, .1. 161/179 3,645,085 2/1972 Rassarl 161/180 3,649,404 3/1972Waterhouse, G. 161/180 Primary E.raminerGeorge F. Lesmes AssistantExaminer-Kendell, Lorraine T.

[57] ABSTRACT A three-dimensionally crimped and twisted syntheticfibrous unit formed by a stem having a relatively large width. Branchesrandomly extend from the stem and have a width less than the sternwidth. and fine hairs randomly extend from the branches. Numerousperipherally and internally formed crevices are provided in the fibrousunit.

3 Claims, 24 Drawing Figures PATENTEB 1 sum 1 0F 7 3.864.903

PATENTED 1 3, 864,903

SHEET 2 0F 7 PATENTEDFEHI 1 I975 3,864,903

SHEET 3 BF 7 FIG.3B

FIG. 4 FIG.5

PATENTEB FEB 1 1 I975 SHEET 0F 7 I DO PATENTED 1 I975 1864.903

SHEET 7 OF 7 1 SYNTHETIC FIBROUS UNIT WHICH IS THREE-DIMENSIONALLYCRIMPED AND TWISTED This is a continuation-in-part of an earlier filedcopending application Ser. No. 24,658 filed Apr. l, I970 and nowabandoned.

The present invention relates to a synthetic fibrous unit of novelconfiguration. This invention more particularly relates to a syntheticfibrous unit having diverse form of branched hairy configurationproduced from one or more synthetic resinous films of a thermoplasticnature by utilizing a draft-fibrillation.

Most of the conventional synthetic fibers are produced by extrudingmaterial polymer solutions or molten material polymers in a filamentaryform through, a spinneret having fine spinning holes of givencrosssectional profiles. Both internally and externally, various typesof cross-sectional features of the filament can be given as desiredthrough modification in the extrusion mechanism and the spinning holescross-sectional profile. But, once the mechanical design is settled, noappreciable variation in the cross-sectional features along the filamentlength can be expected, except indispensable accidental variation in thefineness of relatively minor extent. In addition, unless any particularlater-staged treatment is applied thereto, the produced filaments are inmost cases provided with a remarkably smooth surface when compared withnatural fibers. Such evenness in the cross-sectional feature and smoothsurface leads to degraded inter-fibers frictional property and such apoor inter-fibers frictional property inevitably causes relatively poorcoherency between the fibers composing a yarn.

Further, in the practical mill-production of the synthetic filaments bythe extrusion technique, it is difficult to provide the resultantfilaments with a fineness smaller than approximately 1.0 denier. This isfirstly because of the flow characteristic inherent to the materialpolymer solution or molten material polymer at the time of extrusion andsecondly because of the probable filament breakage after extrusion whichoftentimes takes place due to excessively narrowed spinning holes.Because of this lower limit in the fineness of the produced filament,one cannot so much expect an excellent capillary attraction by thefibrous mass composing, for example, a fabric.

As an attempt to give the filament a threedimensional diversity, thereis the well-known crimping technique. However, even this techniquecannot give a perfect solution to the problem of the superficialsmoothness and the lengthwise evenness in the fineness inherent to theindividual filament.

In order to mitigate the disadvantage encountered in the prior art, amethod of splitting a given synthetic filmy band into a mass of finefibrous units was recently developed. In this method, the givensynthetic filmy band or strip is subjected to a rubbing action bysuitable rubbing means or to a splitting action by suitable splittingmeans such as an inflicting roller or a peripherally screw groovedroller. In case the material filmy band has a relatively large width, itis usual to preliminary slit the band into a plurality of strips ofsmaller width. The obtained fibrous mass is composed of a plurality ofrandomly split fine-fibrous units connected to each other in a networkconfiguration. It is true that this already developed splittingtechnique has, to some extent, solved the problem of the superficialsmoothness and the lengthwise evenness in the fineness of the filamentsobtained. However, as is more apparently proved by the laterdescription, the obtained fibrous unit does not fully meet the generalrequirement for the configurational diversity thereof. Further, in orderto practice this manufacturing, it is necessary to furnish themanufacturing equipment with particular film slitting and/or splittingmeans such as abovementioned. It is also assuredly known that thefibrous units manufactured by the conventional splitting method are notso fine as is suitable for yarns of finer thickness and fabrics of lightand thin construction. For example, the lateral width of the fibrousunits now on the market is at smallest 0.5 mm.

Therefore, it can be concluded that any of the convention'ally developedsynthetic filaments and split fibers cannot assure the provision of thefabric made thereof with sufficient softness, resiliency, warmthretainability, handling quality, bulkiness and hygroscopic property suchas inherent in the fabrics made of natural fibers.

A principal object of the present invention is to provide a syntheticfibrous unit having a remarkably diverse form of configuration andconsiderably fine construction.

Another object of the present invention is to provide a syntheticfibrous unit having an enhanced inter-fibers frictional property.

A still other object of the present invention is to provide a syntheticfibrous unit capable of assuring an excellent capillary attraction tothe fibrous mass composed thereof.

A further object of the present invention is to provide a syntheticfibrous unit capable of assuring a desirable softness, resiliency,warmth retainability, handling quality, bulkiness and hygroscopicproperty which is inherent to the natural fibers of a fabric madethereof.

In view of the above-mentioned objects, the synthetic fibrous unit ofthe present invention is composed of a stem of relatively large width, aplurality of branches randomly integral of the stern and a plurality ofhairs extending at random from the stem and the branches, The entireconfiguration is three-dimensionally crimped and twisted. The fibrousunit is further provided with polygonally-profiled transverse crosssection together with both internally and superficially formed numerousfine crevices.

In the manufacturing of the fibrous unit, one or more synthetic resinousfilms of a thermoplastic nature are firstly subjected to a uniaxialthermal pre-drawing. Thereafter, the uniaxially pre-drawn film or filmsare passed through a draft zone for a draft fibrillation. The draft zoneis formed by two or more pairs of rotational rollers located apart in aprescribed distance and the superficial speed of the downstream rollersis made larger than that of the supstream rollers to such an extent soas to efi'ectuate the purposed draft fibrillation of the given film. [na preferred embodiment. the system includes three pairs of rollers and aparticular mechanical modification may be applied to the intermediateroller pair as later described in detail.

Further features and advantages of the present invention will be mademore apparent from the following description, reference being made tothe accompanying drawings; wherein FIG. IA is an enlarged diagrammaticrepresentation of a fibrous unit of the present invention,

FIGS. 18 and 1C are microscopically enlarged photographicalrepresentations of the fibrous unit of the present invention,

FIG. 2 is a photographical representation of fibrous units of thepresent invention taken in a slackened massed disposition,

FIGS. 3A and 3B are photographical representations of the transversecross sections of the fibrous units of the present invention,

FIG. 4 is an enlarged photographical representation of the transversecross sections of the fibrous units of the present invention,

FIG. 5 is an enlarged photographical representation of the transversecross sections of split fibers manufactured by the conventional filmsplitting method,

FIG. 6 is a partly sectional diagrammatic side view of a basicembodiment of the apparatus of the present invcntion.

FIG. 7 is a diagrammatic side view of another embodiment of theapparatus of the present invention whereon some example tests wereperformed,

FIGS. 8A to 8C are some examples of the staple diagram characteristic ofthe fibrous unit of the present invention,

FIG. 9 is a diagrammatic side view of a modified embodiment of theapparatus of the present invention, wherein a two-stage draftfibrillation is performed,

FIG. I0 is a diagrammatic side view of a practical em bodiment of theapparatus shown in FIG. 9 whereon some example tests were performed,

FIGS. IIA to C are some examples of the staple diagram characteristic ofthe fibrous units of the present invention manufactured on an apparatusshown in FIG. 10,

FIG. I2A is a diagrammatic side view of a practical embodiment of theapparatus of the present invention having three stage successive draftzones,

FIG. I28 is a staple diagram of the fibrous units obtained on theapparatus shown in FIG. 12A,

FIG. 13 is a diagrammatic side view of another modilied embodiment ofthe apparatus of the present invention,

FIG. 14 is a diagrammatic side view ofa practical embodiment of thewith-apron arrangement shown in FIG. 13, whereon an example test wasperformed,

FIG. 15 presents staple diagrams of the fibrous units manufactured onthe apparatus shown in FIG. 14,

FIG. 16 is a diagrammatic plan view of a still another modification ofthe apparatus shown in FIG. 9.

Referring to FIGS. 1A to IC, the fibrous unit of the present inventionis diagrammatically and photographically shown in an enlargedillustration. As is diagrammatically shown in FIG. 1A, the fibrous unitof the present invention is provided with a stem 1 of relatively largewidth, a plurality of branches 2 randomly integral of the stem I and aplurality of fine hairs 3 extending at random from the stem 1 and thebranches 2. The stem I, the branches 2 and the hairs 3 are randomly andindependently crimped and twisted in portions. The diverse form of theentire configuration of the fibrous unit of the present invention can befairly confirmed by the photographs shown in FIGS. IB and IC. It wasconfirmed through the experimental observation by the inventor of thepresent invention that the fineness of the hair 3 in its finest portionwas smaller than 0.2 denier.

This particular diverse form of external configuration cannot be foundin any of the conventional synthetic and natural fibers and it providesa great many advantages when the fibrous units are formed into yarns orfabrics.

In the first place, the randomly crimped configuration of the branches 2causes a sufficient extent of entanglement between the fibrous unitswhen they are massed together. This mutually entangled condition will beunderstood from the graphical illustration shown in FIG. 2, wherein thefibrous units are massed together in a relatively slackened condition.Due to this considerably entangled condition, the coherency of thefibrous units composing the mass is remarkably enhanced and the enhancedcoherency of the fibrous units in the mass assures the production of afine yarn of increased tensile strength and a relatively thin silver orweb of increased tearing strength.

Secondly, the randomly twisted configuration of the fibrous unit bringsabout a desirable increase in the bulkiness of the fibrous mass madethereof. This fairly satisfies the recent public preference for bulkyapparel.

Thirdly, the presence of the numerous fine hairs leads to an enhancedcapillary attraction of the fibrous mass made thereof, which capillaryattraction promises a better hygroscopic property. Therefore, animproved wearing comfort results by using the fibrous units of thepresent invention as a material for fabrics.

Further, because the fibrous unit of the present invention is providedwith the obvious diverse form of configuration such as variation infineness, length, crimp and twist, a textile product made thereof can beaccompanied with functional properties almost the same with thosepossessed by the products made of natural fibers while maintaining theadvantages of the syn thetic fibers such as, for example, an excellentresistance against chemical attack.

In addition to the above-mentioned external configurational features,the fibrous unit of the present invention should be evaluated from aview point of its internal configuration. more particularly from itstransverse cross-sectional features.

Some examples of the transverse cross-sectional fea ture of thesynthetic fibrous unit of the present inven tion are shown in FIGS. 3Aand 38, wherein it is observed that the transverse cross section of thefibrous unit is characterized by a variety of polygonal profiles. It ismicroscopically confirmed that the transverse cross-sectional profilevaries from stem to stem, from branch to branch, from hair to hair, fromstem to branch or hairs and from branch to hairs. This profile having adiverse form in the transverse cross section also, to a great extent,contributes to the enhancement in the inter-fibers frictional propertyto be possessed by the resultant fibrous unit.

As shown most clearly in FIG. 1A the widths or crosssectional dimensionsinvolved show a substantial variation in size when comparing the stem,the branches and the fine hairs. Stem I as particularly illustrated inFIG. 1A has a predetermined cross-sectional dimension of a relativelylarge size as compared to the branches and the fine hairs. Branches 2extend from stem 1 and are seen to have a decreased cross-sectionaldimension as compared to the width of stem 1. Fine hairs 3 extend fromboth the stem and the branches and are seen to be greatly decreased incross-sectional dimension as compared with the widths of both the stemand branches. The term fine hair" is well understood in the art torepresent a most minute cross-sectional dimension as both fine and hair"have well understood meanings of very small, slender elements, and thiscontrast of widths is clearly shown in the FIG. IA illustration.

Further, referring to FIG. 4, an enlarged photographical illustration ofthe transverse cross sections of the fibrous units of the presentinvention is given. As is clearly observed in the drawing, thetransverse cross section is provided with numerous peripherally andinternally formed crevices. The given illustration should be comparedwith the illustration given in FIG. 5, wherein an enlargedphotographical illustration of the transverse cross sections of thesplit fibers manufactured by the conventional splitting process providedwith suitable film inflicting means is shown. By this comparison, itwill be understood that, although the conventional split fibers areprovided with some peripherally and internally formed crevices also,their transverse cross-sectional profiles are remarkably smoother thanthose possessed by the fibrous units of the present invention.

The numerous fine crevices in the fibrous unit of the present inventionassures an enhanced inter-fibers coherency and capillary attraction whenthe fibrous units are massed together to form a textile product.

The reason for the formation of the diverse form of transversecross-sectional profile will be made apparent in the followingdescription.

As a material for the fibrous unit of the present invention, one or morefilms of such synthetic resinous substances such as polypropylene,polyethylene, polyamide, polyacryl, polyester, polyvinylchloride,polyvinylidenechloride and polyvinylalcohol can be advantageously used.

The acquired fibrous units of the present invention are, in a masseddisposition, advantageously used for such textile products as woven orknitted fabrics, nonwoven fabrics, synthetic papers, fishing nets, shockabsorbers, heat insulators, noise absorbers and warmth retainers.

Referring to H6. 6, a principal arrangement of a preferred embodiment ofthe apparatus of the present invention is shown diagrammatically. Theapparatus includes a pair of back rollers 11 and a pair of front rollers12 located apart from the pair of back rollers 11 at a prescribeddistance. The respective pairs 11 and 12 are composed of axiallyrotational top rollers 11a and 12a and axially rotational bottom rollers11!) and 12b disposed in a pressure contact with the corresponding toprollers 110 and 12a. Preferably, the top rollers lla and [2a areperipherally covered by elastic layers lie and 12c for exerting a stablenip on the film and the fibrous units processed through the apparatus.The surface speed of the front rollers 12 is designed as larger thanthat of the back rollers I1 and is, to such an extent, sufficientlycapable of causing a draft fibrillation of the given film. That is, adraft zone 13 is formed in between the pairs of rollers 11 and 12. Onthe apparatus designed as above, one or more uniaxially predrawn film 14is processed through the nips by the roller pairs I1 and 12 and, withinthe draft zone 13, the film 14 is randomly fibrillated into a mass ofnumerous fine fibrous units 15.

The draft-fibrillating mechanism on the apparatus of the presentinvention will now be explained in detail in relation to the resultantdiversity in the configurational features of the fibrous unit obtained.

in the material undrawn film, the film composing polymeric chains areconnected randomly to each other by partial chemical links. Bysubjecting the film of this internal configuration to a uniaxialpre'drawing operation, which is usually performed at a drawing ratio upto 7 or 8, there takes place a compulsive interchains slippage and thechemical links connecting the chains are partially and randomly brokenby this compulsive slippage. In this situation, the film 14 isintroduced into the draft zone 13 and the film 14 is subjected to auniaxial stretching force, which force causes a stress distribution inthe film configuration. This distribution extends three-dimensionallythroughout the films internal configuration. As is above-mentioned,breakage of the chemical links takes place at random location in thefilm configuration. That is, there must be a random distribution ofweak-points throughout the films internal configuration. As iswell-known, when an article having weak-points is subjected to a forceapplication, the stress caused by the applied force tends to concentrateupon the weak-points resulting in the breakage thereof. Once thebreakage takes place at the weakest points, the balance of the stressdistribution is disturbed and the stress tends to concentrate on thesecond weakest points. Breakage of the weakest points is observedexternally as a locational tearing of the film, in other words, alocational fibrillation of the film. Due to the random distribution ofthe weak-points throughout the three-dimensional configuration of thefilm, the above-explained fibrillation takes place at random locationsin the film configuration. With proceeding of the draft action, that is,as the film is transported downstreamly under the above-mentionedcompulsive stretch, the breakage propagates one by one throughout theentire film configuration. Further, at the moment of film breakage at aparticular location of the film, the stress distribution near thatparticular location is suddenly unbalanced and the momentary residualstress in film portions adjacent to that broken location tends to causea random crimping and/or twisting in those film portions. Thus, theresultant fibrous unit of the present invention can be provided withboth a diverse form of branched hairy configuration of randomly andpartially crimped and/or twisted nature and diverse form of profiledtransverse cross section having numerous fine crevices.

For confirmation of the advantages of the present invention, severalmill-scale tests were performed by the inventor of the present inventionand some examples are given as follows.

In all the examples, polypropylene was used as the material polymer. Thematerial polypropylene was extruded into a film of 40 p. thickness and650 mm width. After extrusion, the film was subsequently subjected to auniaxial drawing at a drawing ratio of l0 and temperatures from to l20Cin order to form a uniaxially drawn film of 10 p. thickness and 210 mmwidth.

EXAMPLE 1 A uniaxially drawn film of the above-described nature wasprocessed through an arrangement shown in FIG. 7, wherein the back andfront rollers were somewhat modified in their combination andarrangement Table 1 Average length of the fibrous units in mm I650Effective length of the fibrous units in mm I260 Content of shortfibrous units in 4l.5

Measurement of the values listed in the table was achieved by theanalysis of the obtained staple diagram in a manner generally employedin the cotton mill testing.

EXAMPLE 2 A uniaxially drawn film used in Example I was also processedthrough the arrangement shown in FIG. 7. In this case. however. thedraft ratio was selected as 2.5. The obtained fibrous units wereprovided with desirably diverse form of configurational features and theresult of the staple diagram analysis were as shown in Table 2.

Table 2 Average length of the fibrous units in mm 84.0 Effective lengthof the fibrous units in mm 1320 Content of short fibrous units in l 565EXAMPLE 3 A uniaxially drawn film used in Example I was also processedthrough the arrangement shown in FIG. 7. In this case. however, thedraft zone length was selected as 270 mm and the draft ratio wasselected as 3.2. The configurational features of the fibrous unitsobtained were considerably diverse in form and the result of the staplediagram analysis were as shown in Table 3.

Table 3 Average length of the fibrous units in mm 930 Effective lengthof the fibrous units in mm 168.0 Content of the short fibrous units in70 56.5

Referring to FIGS. 8A to SC, some examples of the staple diagram sampledfrom the mass of the fibrous units of the present invention are shown.The one shown in FIG. 8A corresponds to the fibrous units of Example I.the one in FIG. 88 to Example 2 and the one in FIG. BC to Example 3.From these illustrations, it is observed that the fibrous units of thepresent invention have a staple diagram very similar to thosecharacteristics of natural fibers such as wool. This means that thefibrous unit of the present invention is perfectly distinguished andadvanced from the conventional synthetic fibers in its fiber lengthcharacteristics, also.

EXAMPLE 4 Material polypropylene was formed into a film of IO ptthickness by uniaxially drawing an extruded film at a draw ratio from 7to 8. Next. the uniaxially drawn film was supplied to the arrangementshown in FIG. 6, wherein the draft zone length was selected as 200 mmand the draft ratio was selected as 2.0. The obtained fibrous unit wasprovided with a configuration like that shown in FIG. IA, the maximumfiber length being about 200 mm the average fiber length being about II0 mm and the minimum fiber length being 30 mm. The fineness of the stemwas about [5 denier and that of the finest hair was smaller than 0.1denier. Further, the stem was provided with. in average, from l5 to 20crimps per l inch length and the branches or hairs with, in average.from 25 to 30 crimps per 1 inch length.

Referring to FIG. 9, a modification of the basic arrangement of theapparatus shown in FIG. 6 is diagrammatically shown, wherein two-stagedraft fibrillation is carried out. In the arrangement, three pairs ofrollers II, 12 and I6 are disposed in a mutually spaced apartrelationship. The first draft zone 17 is formed in between the backrollers ll and the intermediate rollers 16 and the second draft zone 18is formed in between the intermediate rollers 16 and the front rollers12. Assuming that the surface speed of the back rollers II is given by Vthat of the intermediate rollers I6 by V and that of the front rollersI2 by V the following relationship is employed in the mechanicaldesigning of the arrangement.

V. v. v.

As to the length of the respective draft zones, it was confirmed thatthe following relationship is established in the mechanical arrangementof the rollers. provided that the length of the first draft zone I7 isgiven by 1, and that of the second draft zone by L In the abovemechanical arrangement. the supplied uniaxially pre-drawn film 14 isfirstly fibrillated to some extent in the first draft zone 17 and next.being introduced into the second draft zone 18, the partly fibrillatedfibrous mass is now subjected to a complete fibrillation so as to bedelivered through the nip by the front rollers 12 in the form of a massof numerous fine fibrous units 15. During the first draft zonefibrillation. numerous crevices are developed in the internalconfiguration of the film and thusly developed crevices assist, to agreat extent. the second zone fibrillation.

Although, only the two-stage draft fibrillation is mentioned in theforegoing description, the abovepresented mathematical relationships (I)and (2) can be well extended to cases wherein three or more stagedfibrillation is performed in succession as follows.

L, L +l wherein V, A surface speed of the i th rollers (counted from theback rollers).

V, A surface speed of the i l th rollers (counted from the backrollers).

L, A length of thej th draft zone, which is formed in between the i thand the i+ l th rollers.

L, l A length of the j 1 th draft zone, which is formed in between thei+ i th and the i 2 th rollers.

Further, through the repeated mill-tests by the inventor, it wasemphatically confirmed that a desirable draft fibrillation effect can beobtained when the following mathematical relationships are mechanicallysatisfied in the arrangement of the apparatus.

EXAMPLE 5 The first draft zone length was selected as 170 mm and thesecond draft zone length as 130 mm. The first draft ratio was selectedas 2.5 and the second as l.7. A mass of fibrous units having variousconfigurational features was obtained and the staple diagram analysisresulted as shown in Table 4.

Table 4 Average length of the fibrous units in mm 60.5 Effective lengthof the fibrous units in mm 93.0 Content of the short fibrous units in52.0

EXAMPLE 6 The first draft zone length was selected as 270 mm and thesecond as 130 mm. The first draft ratio was selected as 2.0 and thesecond as 1.7. The result was as is shown in Table 5.

Table 5 Average length of the fibrous units in mm 68.0 Effective lengthof the fibrous units in mm l2l.0 Content of the short fibrous units in64.5

EXAMPLE 7 The first draft zone length was selected as 270 mm and thesecond as I mm. The first draft ratio was selected as 3.2 and the secondas l.l. The result was as shown in Table 6.

Table 6 Average length of the fibrous units in mm 72.0 Effective lengthof the fibrous units in mm I340 Content of the short fibrous units in68.0

10 The staple diagrams sampled as to the fibrous units of Examples 5 to7 are shown in FIGS. 11A, 11B and 11C in the order of the Examples. Itwill be understood that the fibrous units of the present invention areaccompanied with staple diagrams almost resembling those of naturalfibers such as wool.

EXAMPLE 8 A uniaxially pre-drawn film used in the preceding examples wasprocessed through the arrangement shown in H0. 12A and the mechanicalsetting was as follows:

The first draft zone length in mm 170 The second draft zone length in mm130 The third draft zone length in mm The first draft ratio 2.4 Thesecond draft ratio 1.7 The third draft ratio 2.0

The obtained staple diagram is shown in H08. 128 and the result of theanalysis of the obtained staple dia gram is as shown in Table 7.

Referring to FIG. 13, a modification of the apparatus shown in FIG. 9 isshown, in which modification a pair of apron rollers 19 replaces theintermediate rollers 16. The surface speed of the apron rollers 19 isalso so designed as to satisfy the above-presented relationship (3). Byinserting this apron rollers l9, whipping of the fibrous units at themoment of fibrillation can be effectively prevented and an abrasionalcontract of the apron surfaces with the partly fibrillated film, whichadvances downwardly at a speed approximately similar to the surfacespeed of the front rollers 12, assures further propagated fibrillationof the film. It was further empirically determined that the maximumlength of the resul tant fibrous units are greatly dependent upon thedistance L between the axial line of the main roller of the apron l9 andthe front nip. So, as a sideeffect of using this arrangement, themaximum length of the fibrous units can be changed as desired by onlyadjusting the location disposition of the apron rollers 19 whilemaintaining the location relationship between the back and front rollers11 and 12.

EXAMPLE 9 A uniaxially pre-drawn film used in the preceding examples wasprocessed through the arrangement shown in FIG. 14, wherein the distancebetween the back nip and the apron main roller's axial line was selectedas ISO mm the total draft zone length was selected as 240 mm and thetotal draft ratio was selected as 1.9. For the purpose of comparison,the same type of film was also processed through the same arrangementunder the same processing conditions with the only exception being thatthe apron rollers were removed.

The staple diagrams of the obtained fibrous units are shown in FIG. 15,wherein the curve a is for the withapron case and the curve b is for thewithout-apron case. The result of the staple diagram analysis isillustrated in Table 8. From this result, it is fairly confirmed thatinsertion of the apron roller mechanism has a remarkable effect on thelength of the fibrous units ob tained.

fibrous units in 7;

Referring to FIG. 16, another modification of the apparatus shown inFIG. 9 is illustrated, in which modification a pair of cone roller 20replaces the intermediate rollers 16. As is commonly known, when a coneroller axially rotates, its surface speed at the larger diametralportion is greater than that at the smaller diametral portion. So, inthe present embodiment, the mechanical arrangement must be so designedthat the smallest surface speed of the cone roller 20 is greater thanthe surface speed of the back roller 11 and that the largest surfacespeed of the cone roller 20 is smaller than the surface speed of thefront roller 12. Once a film 14 is supplied to this designed apparatus,the film portion corresponding to the larger diametral portion of thecone roller 20 starts to fibrillate first. This is because of therelatively large difference in the surface speed between the back rollerand the large diametral portion of the cone roller 20. Next, in the zonebetween the cone rollers 20 and the front rollers 12, the film portioncorresponding to the smaller siametral portion of the cone roller 20starts to fibrillate. This is because of the relatively large differencein the surface speed between the small diametral portion of the coneroller 20 and the front rollers 12. Because the largest surface speed ofthe cone roller 20 is designed as smaller than the surface speed of thefront rollers 12, the firstly fibrillated film portion is also subjectedto an additional draft fibrillation while passing through the zone.Thus, a con siderable variation in the fibrillating action can beobtained along the transversal direction of the film.

EXAMPLE A polypropylene film was pre-drawn at a draw ratio from 7 to 8and a uniaxially pre-drawn filament of 0.053 g/cm linear density andabout 900 mm width was obtained. This film was processed through thearrangement shown in FIG. 16. The distances between the three pairs ofrollers were settled as 200 mm. The surface speed of the cone rollers 20were so selected that the draft ratio between the back roller and thelargest diametral end of the cone roller was 2, that the draft ratiobetween the back roller and the smallest diame tral end of the coneroller was 1, that the draft ratio between the largest diametral end ofthe cone roller and the front roller was 1 and that the draft ratiobetween the smallest diametral end of the cone roller and the frontroller was 2.

It was clearly observed that the fibrillation was firstly commenced inthe film portion corresponding to the larger diametral portion of thecone rollers in the first draft zone and the fibrillation propagated tothe remaining film portion in the second draft zone. The film wasperfectly fibrillated into a mass of numerous fine fibrous units ofdiverse form of configurational features.

What I claim is:

l. A synthetic fibrous unit made of a polyolefin consisting of a singlestem having a predetermined crosssectional width, a plurality ofbranches randomly formed integral of said stem, and a plurality ofnumerous fine hairs extending at random from said stern and saidbranches, the entire configuration of said fibrous unit beingthree-dimensionally crimped and twisted at random, said branches havinga decreased crosssectional width as compared with said predeterminedcross-sectional width, said fine hairs having a crosssectional widthgreatly decreased as compared with the cross-sectional widths of saidstem and said branches, and numerous crevices are formed peripherallyand internally throughout said fibrous unit.

2. A synthetic fibrous unit according to claim 1, made from apolyethylene.

3. A synthetic fibrous unit according to claim 1,

made from a polypropylene.

1. SYNTHETIC FIBROUS UNIT MADE OF A POLYOLEFIN CONSISTING OF A SINGLESTEM HAVING A PREDETERMINED CROSS-SECTIONAL WIDTH, A PLURALITY OFBRANCHES RANDOMLY FORMED INTERGRAL OF SAID STEM, AND A PLURALITY OFNUMEROUS FINE HAIRS EXTENDING AT RANDOM FROM SAID STEM AND SAIDBRANCHES, THE ENTIRE CONFIGURATION OF SAID FIBROUS UNIT BEINGTHREE-DIMENSIONALLY CRIMPED AND TWISTED AT RANDOM, SAID BRANCHES HAVINGA DECREASED CROSSSECTIONAL WIDTH AS COMPARED WITH SAID PREDETERMINEDCROSSSECTIONAL WIDTH, SAID FINE HAIRS HAVING A CROSS-SECTIONAL WIDTHGREATLY DECREASED AS COMPARED WITH THE CROSS-SECTIONAL WIDTHS OF SAIDSTEM AND SAID BRANCHES, AND NUMEROUS CREVICES ARE FORMED PERIPHERALLYAND INTERNALLY THROUGHOUT SAID FIBROUS UNIT.
 2. A synthetic fibrous unitaccording to claim 1, made from a polyethylene.
 3. A synthetic fibrousunit according to claim 1, made from a polypropylene.